The present invention relates to a process to purify capacitor grade powders to be used in an electrical energy storage device.
Admittedly, an object to manufacture capacitor/battery grade powders, like tantalum, niobium, aluminum, zirconium, silver oxide, vanadium, magnesium dioxide, CFX, CuO, or any other conventional powder known to those skilled in the art, is to have them extremely purified. These powders, such as tantalum, are obtained from third parties, like H. C. Starck of Newton, Mass., and they require further purification if they are to be used as an electrical energy storage device, like a capacitor for implantable medical devices. A problem with this purification process is that the machines to purify these powders actually contaminate them. The powders are never 100% pure. The machines are normally made of various types of metal, and polymeric materials. As with any machine, wear and tear occurs and these machines shed contaminates into the powders.
If the contaminates are not removed from the powder, they become incorporated into the anode or cathode during the pressing phase. Once pressed into a pellet form, the contaminants generally melt during the sintering process which causes local areas of the pellet to be coated with the contaminants. These areas as a result cause sites of high dc leakage currents and are potential areas for breakdowns during the formation process.
An object of this invention is to avoid contaminates during the purification and manufacturing process of forming an anode and/or a cathode.
Sun in U.S. Pat. No. 4,235,710 discloses a method and apparatus for separating particles using a magnetic barrier. The magnetic barrier system of Sun separates a flowable mixture of particles in accordance with the magnetic susceptibilities of the particles. Likewise, MacElvain in U.S. Pat. No. 4,214,984 discloses an alternative magnetic barrier system.
Neither MacElvain nor Sun disclose separating capacitor grade powders within the purification or manufacturing processes as necessitated by the present invention. Instead, MacElvain uses a magnetic barrier system to separate types of conventional ores, and other metallic substances within his own machine. Likewise, Sun uses his system to separate particulates, like silicon carbide particles from diamond particles as described in Example 3, within his own machine.
As such, the applicants solved this problem of separating contaminates within a purification process of capacitor grade powders.
The present invention is directed to a method of purifying capacitor grade powders. The capacitor grade powder is initially placed into a purifying machine that normally disperses at least one contaminate into the capacitor grade powder. The powder is then placed into a magnetic separation device that separates the at least one contaminate from the capacitor grade powder. The capacitor grade powder is then processed into an electrical energy storage device, wherein the capacitor grade powder has minimal contaminates therein.